It could be the glue, the application technique, or a combination of the two. I would suggest using a thin viscosity adhesive and then rolling the tip on, starting from the free edge back toward the cuticle. This will force out any bubbles.
I would also suggest using a tip without a well or contact area. These tips are applied directly to the free edge and require no blending. Since there is no well or contact area, no bubbles will be seen either. And be careful not to shake the adhesive. Sometimes jostling the glue can cause air bubbles to form. — Lynn Ackerson-Warren is an educator for OPI.